Optical media comprising polyaryl film

ABSTRACT

An optical media comprising a polymeric material film, characterized in that said polymeric material is a polyester obtained from a 9,9-bis(4-hydroxyphenyl)fluorene derivative and a mixture of terephthalic acid and isophthalic acid derivatives, said polymeric material having a glass transition temperature higher than 315° C. and a yellowing coefficient Yc lower than 0.0060.

FIELD OF THE INVENTION

The present invention relates to an optical media comprising an highquality polymeric material film. More in particular, the presentinvention relates to an optical media comprising a polymeric materialfilm having high thermal, mechanical and optical properties.

BACKGROUND OF THE INVENTION

Flat-panel displays (FPD) are becoming increasingly commonplace intoday's commercial electronic devices. FPD in most of their applicationsare expected to be lightweight, portable, rugged, low-power andhigh-resolution. Displays having all these attributes will enable a widevariety of commercial applications in the future.

Most commercially available products use glass as the starting materialin the display fabrication process. Glass has been widely used forseveral optical applications, due to its excellent characteristics, suchas the transparency, the optical clarity, the high transparence in thevisible light range, the high resistance to temperature and thecompatibility with chemicals used in standard semiconductormanufacturing processing. Notwithstanding, due to its high weight andhigh brittleness, the use of glass as support in optical applicationsmay cause problems to the final product realization. In addition,because glass is not flexible, it cannot be used in continuousprocessing, this leading to a relatively low final productivity.

In view of these reasons, it should be desirable to replace glass withtransparent plastic films. If plastic is employed as the startingmaterial for display manufacturing, a display that is not onlylightweight and rugged but also flexible can be obtained. Therealization of such a technology would have a significant impact on thedisplay industry replacing the present sheet processes with a continuousroll-to-roll manufacturing process.

The actual process involved in the display manufacturing are designed towork with the glass support that has excellent thermo-mechanical andoptical properties and that can withstand high temperature processes,solvent treatments and UV-visible light exposure without significantchanges in its properties.

Typical display manufacturing processes, such as those to manufactureliquid crystal display (LCD) and organic light emitting diode (OLED),having an active matrix (AM) or a passive matrix (PM), use the glass assupport, at present. The glass is the starting point for themanufacturing process which comprises the coating of differentfunctional layers which can vary according to the desired kind ofdisplay. Metals or metal oxides such as silicon or indium tin oxide(ITO) are coated on the glass by sputtering or vacuum deposition, forinstance, and then treated by thermal, laser or chemical treatment toform the driving circuit of the display. In case of high performancedriving circuits (TFT, for example) these processes are carried out onglass at a temperature of about 600° C. Recent developments have reducedthis temperature to about 250-350° C. by laser technique.

Most of the plastic materials available in the market, in spite ofhaving optical properties that match the requirements for applicationsas support for display, have glass transition temperature lower than240° C. and this make them useless in the above mentioned processes.U.S. Pat. No. 5,817,550 and U.S. Pat. No. 5,856,858 describe a methodfor the formation of thin film transistors on low-temperature plasticsubstrates. The methods includes the substrate to be coated on bothsides by 0.1-5.0 microns of SiO₂ as first step in the manufacturingprocess. This allow the film to withstand the high temperature requiredby the TFT assembly. N. D. Young et Al., Low Temperature Poly-Si onGlass and Polymer Substrates, ASIA DISPLAY Workshop, 1998 describe thefabrication of polycrystalline silicon TFT on polymer supports. Thermalstability up to 250-350° C. is required to the polymer substrate inorder to obtain TFT's circuits with good properties, such as highmechanical properties and low thermal shrinkage rate to guarantee a goodstability and self-sustaining properties during the constructionprocesses. Further, protective layers are needed to increase theresistance to chemicals and solvents during displays manufacturingsteps.

High mechanical properties are needed to obtain a self-supporting filmduring the device assembly and its use. Eventually, a good resistance tothe UV-visible light exposure without remarkable degradation (supportembrittlement and colour changes) is required to withstand the processsteps where UV sources can be used and to prevent degradation insunlight environment applications.

Other problems are related to the stability during time of the displays.Active materials used in displays are extremely sensitive to oxidationand then to the presence of oxygen and moisture in the internal side ofthe displays. High barrier properties against said oxygen and moistureThe glass accordingly provides a suitable impermeability level for thiskind of applications, while, on the contrary, the plastic generally istoo permeable. This problem, together with the resistance to chemicalsand scratches is solved by adding suitable functional layers to thesurface of the plastic film. Most common anti-scratches layers andbarrier layers are based on UV-photocurable materials and this makes thesubstrate UV resistance one of the main required properties for thepotential plastic support for optical devices. U.S. Pat. No. 6,358,570,U.S. Pat. No. 6,268,695 and U.S. Pat. No. 6,413,645 disclose barrierlayers coated on the plastic film. The main application is as plasticsupport for displays where high barrier properties to moisture andoxygen are required. The barrier structure is a multilayered compositionof curable resins and inorganic compounds. The resins can be cured by UVradiation.

Several patents and patent applications describe fluorene polyestermaterials for electrical applications.

U.S. Pat. No. 3,546,165 describes thermally stable polyesters of variousgem-bisphenols and dicarboxylic acids. Included are polyesters of9,9-bis(4-hydroxyphenyl)fluorene with 100% isophthalic acids and9,9-bis(4-hydroxyphenyl)fluorene with 80% wt isophthalic acid and 20% wtterephthalic acids. Softening temperature of 360° C. for both thesepolymers are reported. UV stability and mechanical properties have notbeen evaluated.

U.S. Pat. No. 4,387,209 describes polyesters made by reacting9,9-bis-(4-hydroxyphenyl)-fluorene with at least one member of the groupconsisting of isophthalic or terephthalic acid and using an interfacialpolymerization process. The polyester inherent viscosity stronglydepends upon the monomer purity and relatively small variations inpurity of the diphenol monomer may cause large deviations in theinherent viscosity values. Polyester films are described to be used inthe electrical insulation field, and neither data on optical propertiesnor possible applications are reported.

U.S. Pat. No. 4,967,306 discloses a9,9-bis-(4-hydroxyphenyl)-fluorene/isophthalic and terephthalic acidpolyester which contains a very low level of low molecular weightoligomers and has a tensile strength, elongation, chemical resistance,temperature stability, ultraviolet resistance and vacuum stabilityhigher than the known in the art co-polymers containing low molecularweight oligomeric species. It is disclosed therein that films containingsmall amounts of oligomer will yellow or degrade upon limited exposureto ultraviolet radiation.

The resin obtained from the polyarylate composed of9,9-bis-(3-methyl-4-hydroxyphenyl)-fluorene and isophthalic acidreported in Journal of Applied Polymer Science, Vol. 29, p. 35 to 43(1984) results to be too fragile and has insufficient abrasionresistance and low film quality.

Japanese Patent Application No. 09-071,640 discloses a resin composed of(a) an aromatic dicarboxylic acid, (b) a specific amount of asubstituted 9,9-bis-(4-hydroxyphenyl)-fluorene and (c) an aliphaticglycol; said resin is utilized in optical materials for its goodtransparency and heat resistance.

U.S. Pat. No. 4,810,771 discloses polyesters made of mono-orthosubstituted bisphenols, and a blend of isophthalic and terephthalicacid.

EP Patent Application 943,640 describes a film prepared withpolyarylates synthesized using bisphenolfluorenes mono- andbi-substituted in the ortho position with alkyl (C₁-C₄) groups. Suchpolyarylates have a better stability to ultraviolet radiation.

9,9-bis(3,5-dibromo-4-hydroxyphenyl)-fluorene bisphenol monomer derivedpolyarylates have been disclosed in PCT Patent Application No. WO00-33,949 as gas-separation membranes.

In U.S. Pat. No. 5,007,945, there is described a polyarylate classobtained from dicarboxylic acid chlorides and cardo bisphenols havinghalo-substituents on all ortho positions of the phenol groups, which isused to separate one or more components of a gas mixture. Such patentsdescribe gas-separation membranes, but do not mention optical filmsconsisting of such polymers.

The present invention describe a plastic film suitable for opticalapplications and more preferably as a display support, able to withstandto the present manufacturing processes and to the enviromentalconditions during its use. Also, the use of a flexible plastic supportwill allow to introduce roll-to-roll technologies in the manufacturingof displays.

SUMMARY OF THE INVENTION

An optical media comprising a polymeric material film, characterized inthat said polymeric material is a polyester obtained from a9,9-bis(4-hydroxyphenyl)fluorene derivative and a mixture ofterephthalic acid and isophthalic acid derivatives, said polymericmaterial having a glass transition temperature higher than 315° C. and ayellowing coefficient Yc lower than 0.0060.

DETAILED DESCRIPTION OF THE INVENTION

An optical media comprising a polymeric material film, characterized inthat said polymeric material is a polyester obtained from a9,9-bis(4-hydroxyphenyl)fluorene derivative and a mixture ofterephthalic acid and isophthalic acid derivatives, said polymericmaterial having a glass transition temperature higher than 315° C. and ayellowing coefficient Yc lower than 0.0060.

The polyester useful in the present invention can be represented by thegeneral structure:

whereinA represents one or more different 9,9-bis(4-hydroxyphenyl)fluorenegroup having general formula (I):

B represents one or more different dicarboxy groups having the formula:

andn is the number of the repeating units which build up the polymer and isa positive integer higher than 20.

Preferably, the present invention refers to an optical film comprisingone or more polyesters represented by the following structure:

wherein n is a positive integer higher than 20. Still more preferably,the present invention refers to an optical film comprising a polyesterobtained from at least two different polymerizable units represented bythe 9,9-bis-(4-hydroxyphenyl)-fluorene group of general formula (I) andfrom a mixture of isophthalic acid and terephthalic acid. Morepreferably, the mixture of isophthalic acid and terephthalic acidcomprises from 20 to 80% by weight of an isophthalic group and from 80to 20% by weight of a terephthalic group. Most preferably, the mixtureof isophthalic acid and terephthalic acid comprises from 30 to 70% byweight of an isophthalic group and from 70 to 30% by weight of aterephthalic group.

When in the present invention the term “group” is used to describe achemical compound or substituent, the described chemical materialcomprises the group, ring and base residue and that group, ring orresidue with conventional substituents. When on the contrary the term“unit” is used, on the unsubstituted chemical material is intended to beincluded. For instance, the term “alkyl group” comprises not only thosealkyl units, such as methyl, ethyl, butyl, octyl, etc., but also thoseunits bearing substituents such as halogen, nitrile, hydroxy, nitro,amino, carboxy, etc. The term “alkyl unit” on the contrary comprisesonly methyl, ethyl, cyclohexyl, etc.

The polymeric material useful in the present invention has excellentmechanical and thermal properties, a high Tg and is less subject toyellowing upon exposure to UV-visible light sources. More in particular,the polymeric material shows a glass transition temperature higher than315° C., more preferably higher than 325° C., and most preferably higherthan 335° C. and a yellowing coefficient Yc lower than 0.0060, morepreferably lower than 0.0055, and most preferably lower than 0.0050.

The above mentioned properties allows the polymeric material of thepresent invention to be used as substitute of glass support in themanufacturing of a number of optical media known in the art, such asliquid crystal displays, electroluminescent displays, organiclight-emitting diode displays, and the like. This allows to obtain moreflexible and resistant displays than those conventionally manufacturedusing glass supports. Also, the use of the polymenic material of thepresent invention allows to use roll-to-roll technologies in themanufacturing of displays.

EXAMPLES

Sample films were obtained by taking compound A and polymerizing it withthe interfacial polycondensation technique as described in EP patent396,418, utilizing a mixture of terephthalic acid (TPA) and isophthalicacid. (IPA) as reported in the following Table 1. TABLE 1 Sample film %TPA % IPA 1 (comparison) 5 95 2 (comparison) 10 90 3 (invention) 30 70 4(invention) 50 50 5 (invention) 70 30 6 (comparison) 90 10 7(comparison) 95 5

The so-obtained polymer was coated with the solvent coating techniqueusing a 10% weight methylene chloride solution of the polymer. Theresulting film having a thickness of 100 μm was then dried for 3 hoursat a temperature of 25° C., gradually increasing the temperature up to amaximum of 160° C. Samples films 1 to 7 were then subjected to UV ageingtests by using a Fusion F300 Lamp System produced by Fusion UV SystemsInc. equipped with H and D bulbs and a 2 mm thick glass pyrex filterinterposed between the UV source and the samples.

Sample film yellowing was measured by comparing their absorbance, beforeand after the expositions, at the selected wavelength of 400 nm whichwas identified as the most significant (blue light absorption). Opticalabsorbance was measured by a Perkin-Elmer Lambda 2 spectrophotometerworking in the 320-500 nm range. The Yellowing Coefficient (Yc) isdefined as the ratio of the averaged variation of absorbance of apolymeric film exposed to a UV radiation source and the effectiveexposure energy. The maximum exposure energy employed was up to 5.0J/cm². The lower is the Yc value, the best is the result. The resultsare summarized in the following Table 2.

The glass transition temperature values (Tg) of the sample films 1 to 7were determined by means of a Perkin-Elmer DSC-4 differential scanningcalorimeter, by following a heating ramp of 10° C./min. starting from atemperature of 50° C. up to 400° C. under a continuous nitrogen stream.The results are summarized in the following Table 2. TABLE 2 GlassFusion System Fusion System Transition H bulb D bulb Temperature SampleYc Yc Tg (° C.) 1 (comparison) 0.00328 0.00299 306 2 (comparison)0.00327 0.00316 308 3 (invention) 0.00375 0.00343 318 4 (invention)0.00446 0.00450 326 5 (invention) 0.00522 0.00541 348 6 (comparison)0.00615 0.00612 363 7 (comparison) 0.00608 0.00664 361

Table 2 clearly shows that only Sample films 3 to 5 are useful in thepresent invention to obtain an optical media having contemporaneouslygood yellowing coefficient values (Yc lower than 0.0060) and good glasstransition temperature values (Tg higher than 315° C.). On the contrary,comparison Sample films 1 to 2 showed glass transition temperaturevalues too low and comparison Sample films 6 to 7 showed yellowingcoefficient values too high.

While a particular embodiment has been set forth to exemplify andexplain the principles of the invention, such are not intended to belimiting. Modifications and changes may become apparent to those skilledin the art, and it is intended that the invention be limited only by thescope of the appended claims.

1. An optical media comprising a polymeric material film, characterizedin that said polymeric material is a polyester obtained from a9,9-bis(4-hydroxyphenyl)fluorene derivative and a mixture ofterephthalic acid and isophthalic acid derivatives, said polymericmaterial having a glass transition temperature higher than 315° C. and ayellowing coefficient Yc lower than 0.0060.
 2. The optical mediaaccording to claim 1, characterized in that said polymeric material hasa glass transition temperature higher than 325° C. and a yellowingcoefficient Yc lower than 0.0055.
 3. The optical media according toclaim 1, characterized in that said polyester is represented by thegeneral structure:

wherein A represents one or more different9,9-bis(4-hydroxyphenyl)fluorene group having general formula (I):

B represents one or more different dicarboxy groups having the formula:

and n is the number of the repeating units which build up the polymerand is a positive integer higher than
 20. 4. The optical media accordingto claim 1, characterized in that said polyester is represented by thefollowing structure:

wherein n is a positive integer higher than
 20. 5. The optical mediaaccording to claim 1, characterized in that said polyester is obtainedfrom 9,9-bis(4-hydroxyphenyl)fluorene and a mixture of terephthalic acidand isophthalic acid.
 6. The optical media according to claim 5,characterized in that said mixture of terephthalic acid and isophthalicacid comprises from 20 to 80% by weight of an isophthalic group and from80 to 20% by weight of a terephthalic group.
 7. The optical mediaaccording to claim 5, characterized in that said mixture of terephthalicacid and isophthalic acid comprises from 30 to 70% by weight of anisophthalic group and from 70 to 30% by weight of a terephthalic group.